|By Matt Spetalnick and Andrew Cawthorne

|By Matt Spetalnick and Andrew Cawthorne

WASHINGTON D.C./CARACAS (Reuters) - The Trump administration is preparing sanctions against several senior Venezuelan officials, U.S. officials said on Tuesday, to pressure President Nicolas Maduro to abort plans for a controversial congress foes say would cement dictatorship.

Maduro's leftist government vowed on Tuesday, however, to proceed with the July 30 vote for the new Constituent Assembly, roaring back at what it called a "brutal interventionist" threat from its ideological foe in the north.

President Donald Trump said on Monday he would take "strong and swift economic actions" if Maduro went ahead with the new body that would have power to rewrite Venezuela's constitution and supersede other institutions.

Those sanctions could be rolled out as early as Tuesday, one of the officials told Reuters, but may be delayed as Trump's administration reviews all its options.

The sanctions would freeze the officials' U.S. assets and prohibit anyone in the United States from doing business with them. It would be the first phase of new actions the Trump administration is considering, including possible targeted sanctions against Venezuela's vital oil sector.

Venezuela is the third largest foreign oil supplier to the United States, after Canada and Saudi Arabia, exporting about 780,000 barrels per day of crude.

While that could bankrupt the Maduro administration and worsen already grave food shortages, hitting Venezuela's energy sector could also raise U.S. domestic gasoline prices, which would be unpopular with Americans.

Any sanctions by Trump, who is largely unpopular abroad, could be used by Maduro to bolster his accusations that Washington is trying to sabotage leftism in Latin America and unite the ruling Socialist Party just as fissures were emerging.

'XENOPHOBIC THREAT'

Decrying "imperialism" still resonates for some in a region scarred by Washington's support of coups during the Cold War.

"Venezuelans are free and will unite against the insolent threat from a xenophobic and racist government ... (and) the United States' brutal interventionist efforts," Foreign Minister Samuel Moncada said on Tuesday, vowing the July 30 vote would go ahead.

"It is an act of political sovereignty by the Republic. Nothing and nobody can stop it," he told reporters.

Polls show a majority of Venezuelans oppose the Constituent Assembly, which critics say would be elected in a sham poll.

Maduro insists it is the only way to bring peace after months of anti-government unrest that has killed 100 people and further hurt a crippled economy.

Maduro's opponents say they drew 7.5 million people onto the streets at the weekend to vote in a symbolic referendum where 98 percent disagreed with the assembly plan.

Calls to cancel the assembly and instead hold conventional elections have come from around the world, including the European Union and major Latin American nations.

The ruling Socialist Party would likely be thrashed in any normal vote due to widespread anger over economic hardships.

"The Constituent Assembly should be abandoned to achieve a negotiated, safe and peaceful solution in Venezuela. The whole world is asking for that," Colombia's President Juan Manuel Santos tweeted.

Venezuelan opposition supporters have been in the streets for nearly four months demanding a presidential election, freedom for several hundred jailed activists, independence for the National Assembly legislature, and foreign aid.

Protesters blocked roads in parts of Caracas on Tuesday, and a national strike was planned for Thursday.

(Additional reporting by Diego Ore, Andreina Aponte, Alexandra Ulmer and Girish Gupta in Caracas, Marianna Parraga in Houston, John Walcott in Washington; Writing by Andrew Cawthorne and Alexandra Ulmer; Editing by David Gregorio and Andrew Hay)